Jose Mourinho says the "hearts and minds" of everyone at Manchester United are with those affected by the horrific attack that killed 22 people and injured many more.
Twenty-two people were killed, including children, and 59 wounded in an explosion at the end of a concert by US singer Ariana Grande in Manchester last night.
British police say the attack at Manchester Arena was carried out by one man who detonated a device he was carrying.
In the wake of the incident, UEFA accepted United's formal request to cancel their press conference ahead of the Europa League final, while the team held a minute's silence at training before flying to Sweden.
The Islamic State terror group has claimed responsibility for a bombing that United manager Mourinho says dominates their thoughts ahead of facing Ajax in Stockholm.
"We are all very sad about the tragic events last night; we cannot take out of our minds and our hearts the victims and their families," the Portuguese said.
"We have a job to do and we will fly to Sweden to do that job. It is a pity we cannot fly with the happiness that we always have before a big game.
"I know, even during my short time here, that the people of Manchester will pull together as one."
UEFA has expressed its shock and sadness at the incident, but insists there is "no specific intelligence" to suggest the final may be the target of an attack.
A statement from European football's governing body in the wake of the Manchester attacks read: "There is currently no specific intelligence which might suggest that any of the UEFA Europa League Final activities in Stockholm may be the target of attacks.
"UEFA has been closely working with local authorities and the Swedish FA for many months and the terrorist risk had been taken into account since the very beginning of the project.
"Furthermore, a number of additional security measures were implemented following the attacks in Stockholm last April.
"Due to the tight security arrangements, UEFA urges fans to arrive at the stadium as early as possible, as detailed checks will be made at the entrances, resulting in potential delays in accessing the stadium."
"Can't believe what happened last night," defender Daley Blind said. "My thoughts go out to all those affected. #PrayForManchester"
United's Ashley Young posted: "Absolutely shocked to hear the news this morning. Thoughts with all that lost loved ones & prayers for those being treated in hospitals"
Earlier winger Jesse Lingard said: "My thoughts and prayers are with everyone affected by last nights attack on this beautiful city. We will stand together in this dark hour Gn+"
City players past and present also posted their sympathy.
"Shocking events for this great city," Raheem Sterling said. "My thoughts and prayers are with the families."
City captain Vincent Kompany posted: "I would like to express my deepest condolences to the families of the victims. It's a sad day for the great city of Manchester. #Unity"
Greater Manchester Police have set up a help centre for anyone needing assistance at Gate 11 of City's Etihad Stadium.
There is no news yet on how United might pay tribute in the Europa League final, but England are wearing black armbands for the Tuesday's match against Guinea at the Under-20s World Cup.
